Whole body vibration, as the name suggests, refers to mechanical oscillations which are applied to the entire body as opposed to a localised application. Recently this principle has been used in the fitness and physical therapy fields in the form of vibration training.
In vibration training the user may stand or otherwise make contact with a vibrating platform and their musculo-skeletal system is exposed to high speed oscillations causing a range of muscles to contract and relax on a continuous basis thereby building and strengthening muscle. Vibration training also provides substantial therapeutic benefits in terms of increasing bone density, aiding mobility and improving tissue perfusion, to name but a few.
There are three factors to be considered in designing vibration training machines and these are the amplitude of the displacement of the platform, being the distance travelled between two points, the frequency of the oscillations, being the number of oscillations per second, and the G force, being the acceleration of the displacement felt by the user which ultimately determines the magnitude of the load applied to the muscles. These factors are inextricably linked and so, for example, if a vibration machine has a small amplitude of displacement of its vibration platform then a higher frequency of vibrations will be required to provide the same G force as is achieved by a machine with a platform having a greater amplitude of vibration.
There are currently two different types of vibration training machines, the lineal and pivotal forms. Lineal vibration machines have a vibration platform which simply moves vertically up and down between two points, much in the manner of an elevator. Some lineal machines allow displacement modulation whereby the user may have a choice of, typically, two settings. This may allow for a ‘low’ setting whereby the amplitude of displacement of the platform is, typically, 2 mm and a ‘high’ setting with a vibration amplitude of, typically, 4 mm.
Lineal vibration, because of its relatively small amplitude of vibration, typically operates at relatively high frequencies (25-50 Hz) to achieve a useful working G force. However, for use by elderly people the displacement can be kept low to produce a low G force thereby making the machine safer for this group. Lineal machines thus provide some advantages in terms of control over G force applied to the user. The main drawback associated with lineal machines is that the nature of the movement they produce means that the transmission of vibrational mechanical energy to the head is quite keenly felt by the user. This results in many users finding lineal machines too uncomfortable to use for extended periods of time, due to the onset of headaches, neck pain etc, and raises concerns about their safety.
The second type of vibration training machine is a pivotal machine in which a pivotal vibration platform oscillates around a central fulcrum, much in the manner of a see saw. Pivotal machines do not provide for displacement modulation per se in the manner of the lineal machine but a user can adjust the amplitude of displacement they are exposed to by moving their stance to be closer to or further away from the fulcrum. This is not entirely satisfactory because when performing certain exercises on the platform the contact points the user makes with the platform need to be a certain distance apart. For example, when performing a push up the user's hands would be roughly shoulder width apart and so placed at opposite ends of the platform and exposed to the maximum displacement amplitude which may be excessive. If a lower displacement amplitude is required the distance between the user's hands, and the exercise position, may need to be altered such that the exercise becomes less effective or even impossible for the user to complete. It is, therefore, more difficult for a user to control the G force they experience during pivotal training.
Since the displacement of a pivotal platform can be up to about 13 mm they tend to operate at lower frequencies than lineal machines to achieve a similar G force output. Further, with a displacement of up to 13 mm, it is difficult to produce an effective low G force pivotal machine for use by the elderly or infirm because of the large amplitude of vibration which cannot be completely offset by a low frequency and still maintain efficacy. Users do report that a pivotal machine has a more comfortable feel in terms of vibration transmission to the head and research has shown that the magnitude of vibration felt in the head region is dramatically lower than for lineal machines.
There is a need for a vibration training machine which can operate over a range of G force output and which avoids at least some of the disadvantages mentioned above.